1. Field of the Invention
The present invention relates to a recording apparatus and a recording method, and more specifically to a recording apparatus and a recording method used in information processing equipment such as printers, copying machines, facsimiles, word processors and computers.
2. Description of Related Art
A recording apparatus has been known, in which a plurality of recording elements, such as ink discharging elements each comprising an ink nozzle capable of ejecting individual ink droplets, a liquid path and a discharge energy generating element, are arranged in a recording head with a precise predetermined density, and in which the recording head mounted in a carriage, while traveling in a main scan direction, selectively ejects ink droplets from the ink nozzles onto a recording material to make ink recording in a height corresponding to the arrangement length of nozzles, followed by the recording material being fed in a sub-scan direction perpendicular to the main scan direction, with the above process repeated to make desired recording.
Such a conventional recording apparatus is known to have a recording head with 128 ink nozzles arranged at a pixel density of, for example, 360 dpi and to perform recording at a pixel density of 720 dpi, two times that of nozzle arrangement density. By referring to FIGS. 11 and 12, the configuration of a sheet feed drive transmission system in the conventional recording apparatus and the operation performed to realize recording will be explained.
In FIG. 11, designated 101 is a sheet feed motor, a pulse motor that makes one turn in 96 steps. A motor gear 102 is coaxial with the motor 101 and meshes with a slowdown large gear 103. A small gear 104 coaxial with the slowdown large gear 103 meshes with a sheet feed roller gear 105 to reduce a rotating speed of a sheet feed roller 106. The number of teeth (=Z) is set to 12 for the motor gear 102, 60 for the slowdown large gear 103, 20 for the small gear 104, and 60 for the sheet feed roller gear 105. The diameter of the sheet feed roller 106 is set to 16.17 mm.
Based on the above setting, the distance that a sheet is fed by each step of the sheet feed motor 101 and the distance that a sheet is fed by each turn of the motor are calculated as follows.
The distance that the sheet is fed by one step of the motor EQU =.pi..times.16.17.times.20/60.times.12/60.times.1/96 EQU .congruent.0.0353 mm=35.3 .mu.m=1/720 inch
The distance that the sheet is fed by one turn of the motor EQU =.pi..times.16.17.times.20/60.times.12/60.congruent.3.3888 mm
That is, the amount of feed for one step of the sheet feed motor 101 corresponds to the pixel density of 720 dpi.
A conventional recording operation, in which with a sheet fed by the sheet feed motor 101 through drive gears, the recording head having 128 ink nozzles arranged at a pixel density of 360 dpi performs recording at a pixel density of 720 dpi, will be explained by referring to FIG. 12.
In FIG. 12, A to C each denotes an array of recorded dots (pixels) produced during three main scans by ink ejecting from 128 nozzles that are arranged at a pixel density of 360 dpi. E represents an amount of sub-scan performed between the main scan recordings of dot array A and dot array B, and F represents an amount of sub-scan performed between the main scan recordings of dot arrays B and C. That is, the amounts of sub-scan E and F are so set that the starting recorded dot of array B is positioned between recorded dots No. 64 and 65 of the array A and that the starting recorded dot of array C is spaced a certain distance from the recorded dot No. 128 of array A and positioned between the recorded dots No. 65 and 66 of array B.
That is, the amount of sub-scans E and F are, as shown in FIG. 12, 4.4803 mm and 4.5508 mm, respectively. Three main scan recordings and two sub-scan operations produce recorded dots shown at array D, which has a 720-dpi dot density at overlapped recorded portions between the arrays A and B and between the arrays B and C.
As described above, after each recording operation in the main scan direction by the recording head with 128 ink nozzles arranged at a 360 dpi pixel density, the sheet is fed in the sub-scan direction either by 127/720 inch (i.e., 127 steps) or 129/720 inch (i.e., 129 steps), which are alternated, thus achieving recording at a 720 dpi pixel density.
With the conventional recording apparatus, however, because the 360-dpi recording requires repeating only a 128/360-inch sheet feed, what is required of the sheet feed motor 101 is a performance of 48 steps/turn, with one step corresponding to the sheet feed of 1/360 inch. To realize a 720-dpi recording, however, requires two kinds of sheet feed-a 127/720-inch feed and a 129/720-inch feed-to be performed alternately, as described above. This requires the use of an expensive sheet feed motor 101 with a capability of 96 steps/turn to make one step match 1/720 inch. Another problem is that if the minimum feed can be made to match a 1/720 inch by changing the motor, a stop position is not accurate enough. For example, in FIG. 12, after the main scan recording is finished for the dot array A, a 127/720-inch sheet feed must be performed to place the nozzle corresponding to the dot No. 1 of array B 1/720 inch below the position of the dot No. 64 of array A. The distance between dot No. 64 and No. 65 is mere 70.6 .mu.m and a sheet feed precision required is at least about .+-.20 .mu.m.
A commonly used pulse motor is what is generally called a four-phase motor which, when it stops in response to an input pulse, is known to shift its stop position in a four-step cycle. In the conventional recording apparatus such as described above, a 127-step input and a 129-step input are alternated. If we let the four phases be A, B, C and D and the motor is started from phase A, the motor stops at phase A and phase D alternately, increasing errors in the stop position.
Because the sheet feed motor gear 102 is fitted tightly over the motor shaft, it naturally makes a whole turn in 96 steps. Hence, the stop position for the 127-step and 129-step inputs apparently changes to 31 steps (=127-96) and 33 steps (=129-96) alternately. This means that in each sheet feed operation, where the motor gear 102 stops can be said to be virtually random. Further, a general problem is that if a certain rotation angle is to be transmitted, errors called "meshing errors" are caused by imperfect finish of the gear contours. This also adds to the sheet feed position errors.
It is conceivable to add another reduction gear in the drive system and change the reduction ratio to make one step of the sheet feed motor 101 match the 1/720-inch feed. In this case, however, the increased number of gears involved in the drive force transmission will increase the transmission errors.
As described above, with the conventional recording apparatus, when it is attempted to increase the recording density, the image produced is likely to be disturbed by poor sheet feed position precision.